In your HTML code, identify the HTML element that holds the text you want to modify. If you only want to modify the font size of a portion of a larger element (a "p" or "div," for example), you can elect to enclose the length of it in a "span" element.

Add the "style" attribute to the element

If the HTML element does not already have a "style" attribute, add it to the opening HTML tag by inserting ' style="" ' between the its name and the greater-than symbol. Set your cursor between the double quotation marks. Otherwise, if the HTML element already has a "style" attribute, set your cursor directly after the first double quotation mark of the existing "style" attribute.

Add the "font-size" property

Type "font-size: " and then add the desired font size value after it. Terminate the CSS property by adding a semicolon after the value. The inserted style attribute should resemble ' style="font-size: 12px;" '.

Save your code and test the changes

Save your code. If your page was already open when you made the modification, you must reload it to see any meaningful changes.